The present invention relates to a turbine nozzle as employed in a multi-stage turbine of a gas turbine engine, and more particularly, a supporting and sealing structure for an array of radially extending guide vanes of a turbine nozzle wherein the root ends of the guide vanes are flexibly connected by a segmented inner shroud, and which supporting structure includes a pressure dam to minimize the amount of leakage introduced by providing flexibility in the nozzle assembly.
In a multi-stage turbine of a gas turbine engine, stationary vane assemblies are inserted between the rotor wheels, as well as at the entrance and exit of the turbine unit. In the operation of the gas turbine engine, the stationary vane assemblies function to alter the static pressure and change the velocity of the high pressure, high temperature gases flowing through the turbine. Heretofore, in order to insure the structural integrity of a vane assembly as it is subjected to thermal excursions of the components of the assembly during transient and steady state operating conditions of the gas turbine engine, it has been common to cast the entire nozzle assembly in one piece. The one piece assembly included an outer, unitary shroud, an inner, unitary shroud, and the array of radially extending guide vanes. With this prior art construction, it has been found that during transient and steady state operation of the gas turbine engine, the temperature differentials between the thin, fast responding vanes and the slower, more massive shroud rings, causes a differential thermal growth or thermal gradient to develop within the nozzle assembly, as well as different temperature levels throughout the nozzle assembly. The result of the differential thermal gradients causes differential thermal excursions of the parts of the nozzle assembly, thereby leading to the development of local stresses and cracks in the interconnections between the vanes and the shrouds. In addition, the inner shroud of a stationary turbine nozzle is usually sealed by a sheet metal member which is usually brazed to the inner shroud, and it has been found that the thermal excursions of the parts of the turbine nozzle have caused distortion and separation of the brazed connections due to the thermal loading on the sheet metal pieces, thereby resulting in pressure leakage through the vane assembly.
Accordingly, it is an object of the subject invention to overcome the shortcomings of the prior art turbine nozzle assemblies and to provide a new and improved supporting and sealing structure for an array of radially extending guide vanes of a nozzle of a gas turbine engine, which supporting and sealing structure provides a flexible coupling between the individual vanes and the inner shroud.
It is another object of the present invention to provide a new and improved supporting and sealing structure for an array of radially extending guide vanes of a gas turbine engine wherein the flexible coupling between the root ends of the vanes and the inner segmented shroud is sealed by a flexible, pressure dam to minimize leakage through the flexible coupling.
It is a further object of the present invention to provide a new and improved supporting and sealing structure for an array of radially extending guide vanes of a nozzle of a gas turbine engine including means for maintaining the radial and axial alignment of the vanes under transient and steady state operating conditions of the gas turbine engine.